The present specification provides a method for performing wireless power reception by a wireless power receiver in a wireless power transmission system, and a device using the method, the method comprising: transmitting information related to a power transfer contract to a wireless power transmitter; generating the power transfer contract with the wireless power transmitter on the basis of the information; and receiving the wireless power from the wireless power transmitter on the basis of the power transfer contract, wherein the wireless power receiver transmits the information to the wireless power transmitter on the basis of an amplitude shift keying (ASK) signal, and the ASK signal is generated on the basis of an input signal based on pulse width modulation (PWM).